<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			.a {
				display: flex;
				margin: 0 auto;
				width: 80%;
				height: 500px;
				background-color: pink;
				flex-direction: row;
				/* justify-content: center; */
				align-content: flex-start;
				flex-wrap: wrap;
			}
			.a div {
				width: 100px;
				height: 50px;
				background-color: blue;
				border: 1px solid red;
			}
			.b {
				position: relative;
				top: 10px;
				margin: 0 auto;
				width: 80%;
				height: 500px;
				background-color: pink;
			}
			.b div {
				float: left;
				box-sizing: border-box;
				width: 33.33333333333%;
				height: 100px;
				max-width: 100px;
				min-width: 50px;
				background-color: green;
				border: 1px solid red;
			}
		</style>
	</head>
	<body>
		<div class="a">
			<div>1</div>
			<div>2</div>
			<div>3</div>
			<div>4</div>
			<div>5</div>
			<div>6</div>
			<div>7</div>
			<div>8</div>
			<div>9</div>
			<div>10</div>
			<div>11</div>
			<div>12</div>
			<div class="last">13</div>
		</div>
		<div class="b">
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
			<div>1</div>
		</div>
	</body>
</html>
